Process for the production of metal soaps

ABSTRACT

A process for the production of a solid metal soap of the formula 
     
         M(R--COO)(R&#34;--COO) 
    
     in which M is at least one metal from the group of Ca, Mg, Cd, Ba, Zn, and Pb; and R and R&#39; are C 8  -C 34  hydrocarbon radicals, by direct synthesis from at least one fatty acid with metal oxides and/or metal hydroxides which comprises maintaining a reaction zone containing a liquid phase comprising fatty acid under reduced pressure, passing a portion of the liquid phase to an external premixing zone, introducing a solid metal oxide and/or metal hydroxide into the liquid phase in the premixing zone, passing the mixture to the reaction zone through an intensive mixing zone, and continuously removing water of neutralization formed by the reaction.

FIELD OF THE INVENTION

This invention relates to a process for the production of solid, neutralor basic metal soaps by a controlled solid/liquid reaction of liquidfatty acids with solid metal oxides and/or metal hydroxides in anexternal premixing zone under reduced pressure and to the use of themetal salts as a stabilizer and/or lubricant mixture in the processingof plastics.

BACKGROUND OF THE INVENTION

It is known that metal soaps are produced either by the melt process, inwhich the molten fatty acid is reacted with metal oxides, hydroxidesand/or suitable metal salts, or by the precipitation process in whichtheir sodium soaps are subjected to double decomposition withwater-soluble salts of the corresponding metals. The precipitationprocess generally gives very clean and voluminous products which can beprocessed at temperatures below 100° C. However, filtration and dryingcosts make it much more expensive than the melt process.

Stabilizers produced by the melt process are satisfactory in purity andcolor for many industrial applications, for example as stabilizers inthe processing of plastics. For example, the lead, barium and cadmiumcompounds have been successfully used in practice as such stabilizers.However, these substances have a highly toxic effect, particularly whenthey are present in powder form. Dust emission, particularly duringprocessing, is a particular hazard to manufacturers of powder-formstabilizers because the powder-form metal soaps are taken up by therespiratory system and are able to develop their toxic effect therein.

RELATED ART

For these reasons, melt processes are described in DE-PS 15 44 697 andDE-PS 17 94 429 which, to prevent dust emission, claim astabilizer/lubricant combination consisting of a mixture--combined inthe melt--of a purely organic component suitable as lubricant, forexample an ester of wax acids and higher aliphatic alcohols, paraffinsor fatty alcohols, a suitable metal soap, a long-chain aliphaticcarboxylic acid or basic lead salts of inorganic or organic acids. DE-PS15 45 697 in particular describes a process for the production of thesedust-free stabilizer/lubricant combinations, in which the toxic,insoluble dust-form stabilizers are dispersed in melts of the lubricantsor in molten mixtures of stabilizers and lubricants and are convertedinto the solid state either on a flake-forming roller or by simpledischarge into pans. The powder-form toxic stabilizers are completelyenveloped in the non-toxic lubricants by this process. They are presentin solid form and are completely dust-free because the lubricantsnaturally have considerably better adhesion than the powder-formstabilizers.

In addition, EP-A 163 395 and GB-A 2,113,521 describe processes for theproduction of animals feeds in which liquid or molten fatty acids arereacted with calcium oxide or calcium hydroxide in the presence ofproteins and carbohydrates. However, these processes are very expensiveon equipment because the reaction mixture, which evidently does notreact off completely, has to be spread out on an endless belt or thelike for after-reaction and drying. The calcium soaps obtained in thisprocess would appear to be difficult to convert into free-flowingparticles without the additives mentioned above, such as proteins orcarbohydrates.

Finally, applicants' DE-OS 38 06 192 describes a process for theproduction of powder-form basic metal soaps, in which powder-form fattyacids are reacted with powder-form metal oxides or metal oxide mixturesin the presence of water or an acid as catalyst at temperatures fromambient temperature to 100° C., optionally under reduced pressure, thereaction mixture having to be present throughout the reaction in theform of discrete free-flowing particles.

Now, the problem addressed by the present invention was to provide animproved process for the production of powder-form, neutral or basicmetal soaps which would provide for dust-free, environmentally safeintroduction of the solid metal oxide or metal hydroxide into the fattyacid melt in the form of a controlled solid/liquid reaction without theaddition of a catalyst. Another problem addressed by the presentinvention was to provide a process for working up the liquid metal soapswhich would enable the water of neutralization formed to be readilyremoved under process conditions via a suitable condensation unit.

BRIEF DESCRIPTION OF THE INVENTION

The technical solution to the problem addressed by the present inventionis based on the concept of removing parts of the fluid phase of thefatty acid mixture initially introduced from the contents of the reactorunder process conditions and delivering them to a premixing zone intowhich the solid metal oxide and/or hydroxide is introduced. In thispremixing zone, a mixture is formed from the circulated liquid phase andthe solid phase introduced and is adjusted in its consistency so thatthe mixture may function as a so-called "living seal". By establishingsuitable reaction conditions for the solid reactants to be introducedinto the interior of the reactor kept under reduced pressure, thepressure inside the reactor can be reliably controlled with regard tofoaming. After the solid has been introduced, the reaction space of thepremixing zone can be closed by suitable mechanical elements so thatoutside air cannot be admitted into the reaction system.

Accordingly, the present invention relates to a process for theproduction of solid, neutral or basic metal soaps corresponding to thefollowing general formula

    M (R--COO)(R.sup.1 --COO)

in which M represent one or more metal cations from the group consistingof Ca, Mg, Cd, Ba, Zn and Pb and R and R¹ may be the same or differentand represent C₈₋₃₄ hydrocarbon radicals, by direct synthesis from acorresponding fatty acid or fatty acid mixture with metal oxides and/ormetal hydroxides, characterized in that a stream of the liquid phase ofa fatty acid or fatty acid mixture kept under reduced pressure in thereactor is run off into an external premixing zone and contacted thereinwith a solid metal oxide and/or metal hydroxide in a solid/liquidreaction, the reaction product formed is returned to the reactor via afollowing intensive mixer and the water of neutralization formed iscontinuously removed from the reactor via the gas phase.

The advantages of the process according to the invention lie on the onehand in the exact dust-free and, hence, environmentally safeintroduction of the metal oxides or metal hydroxides into the fatty acidmelt, so that the reactor capacity can be better utilized throughrelatively low foaming, and on the other hand in the fact that, incontrast to the prior art, there is no need to add a catalyst. Anotheradvantage of the process according to the invention is that the metalsoaps returned to the reactor do not have to be subjected to atime-consuming after-reaction because the neutralization reaction hasalready taken place completely in the external reaction loop.

DETAILED DESCRIPTION OF THE INVENTION

In one preferred embodiment of the invention, the liquid/solid reactionaccording to the invention is carried out in such a way that theexternal premixing zone before the intensive mixer is in direct pressureequalization with the reduced pressure prevailing inside the reactor andat the same time--via the feed system for the solids--with the ambientpressure and the consistency of the paste-form mixture formed in thepremixing zone is selected so that the mixture serves as a sealingcompound for pressure equalization.

According to the invention, the melt of the fatty acid or fatty acidmixture is run off into the external premixing zone under a reducedinternal reactor pressure of approximately 100 to 900 mbar andpreferably 200 to 800 mbar, the internal pressure in the premixing zonehaving to be reduced to take the fall in pressure into consideration. Inthe premixing zone, the fatty acid melt is contacted under reducedpressure--optionally several times--with at least stoichiometricquantities of metal oxide and/or metal hydroxide in a solid/liquidreaction.

Accordingly, a considerable difference in pressure prevails between theinterior of the reactor and the atmospheric pressure. The mixtureserving as a "living seal" in the premixing zone therefore has to beadjusted in its consistency so that, under the particular conditionsprevailing, it is able to act as an actual sealing element againstpenetration of the far higher external pressure into the interior of thereactor. This threat to the desired pressure equalization is not theonly burden on the paste-form sealing compound. To prepare the mixture,the liquid component has to be introduced into the premixing zone undera limited elevated pressure. If the liquid pressures are too high, partsof the liquid phase are in danger of breaking through the powder-formmetal oxide and/or metal hydroxide introduced--preferablycontinuously--from "outside". Accordingly, this is a second source ofdanger to the desired trouble-free, preferably continuous section of theprocess where the solid reactants are introduced into the reactor undertime control.

To rule out interruptions of the type just mentioned, a preferredembodiment of the process according to the invention is characterized inthat the premixing zone is also operated under reduced pressure.However, the reduced pressures prevailing therein are higher bycomparison with the reduced pressure prevailing inside the reactor. Thepressure in the premixing zone is preferably kept at around 400 to 900mbar and, more preferably, at around 750 to 850 mbar. This pressurerange is established by adapted control of the streams of liquid andsolid material to the premixing zone and their discharge into theinterior of the reactor. Selected mass ratios of the streams of liquidand solid reactants have proved to be advantageous for forming themixture acting as a living seal in the premixing zone. The preferredmass ratios of the liquid phase (m₁) to the solid reactants (m₂) are inthe range from about 20:1 to 100:1. Mass ratios of m₁ to m₂ ofapproximately 30:1 to 80:1 have proved to be particularly suitable.

In applicants' above-cited earlier application DE-OS 38 06 192, it ispointed out that the particles should be present in discretefree-flowing form during the reaction. Accordingly, it is proposed (theteaching of the present invention in its preferred embodiment also makesuse of this) to subject the mixture of active substances initiallyformed to fine dispersion under the effect of suitable technical mixingelements. So-called inline mixers, for example operating on thestator/rotor principle, have proved to be particularly suitable for thispurpose. More particularly, that unit of the reactor installation whichis affected by the process according to the invention is designed, forexample, as follows:

A premixing zone is provided separate from the main reaction zone, butin direct pressure communication with the main reaction zone. The dry,preferably powder-form, solid reactant is delivered to the premixingzone, preferably by a screw conveyor. At the same time, liquid phase inadmixture with the solid reactant introduced is added to the premixingzone from the interior of the reactor through a circulation pipe so thatthe mixture acts as a living seal in the premixing zone (particularly inthe region of the stated mass ratios of liquid phase to solid phase).From the premixing zone, the paste follows the pressure gradient towardsthe interior of the reactor and enters the intensive mixer, i.e. forexample the following inline mixer, which it then leaves to enter theinterior of the reactor. The rate at which the material passes throughthe premixing zone can be controlled virtually as required under theseconditions and optimally adapted to the course of the reaction insidethe reactor. The solid reactants may be added in batches and/orcontinuously.

After the solid reactants have been introduced, the interior of thereactor is closed off from its surroundings. This can be done, forexample, by a separating element provided in the premixing zone whichseparates the premixing zone and the screw conveyor for the solidmaterial from one another. During introduction of the solid reactants,the separating element is opened. After the total quantity of solidreactants required has been added, it is closed again.

In one particularly preferred embodiment of the invention, the solidmetal oxide or metal hydroxide is introduced into the fatty acid melt bymeans of an inline mixer which meters the fatty acid mixture at a rateof approximately 1 to 20 m³ per hour and the solids at a rate of 50 kgto 500 kg per hour and preferably 100 to 300 kg/h. In order to guaranteemaximum transport capacity of the inline mixer, the pressure of theinstallation has to be varied so that the fatty acid melt does not flowback into the space of the screw conveyor for the solid material.

According to the invention, the solid metal oxide and/or metal hydroxideare introduced into the fatty acid melt in such a way that the particlesize of the agglomerate formed is below 10 μm and the acid values of themetal soaps formed are between 0.1 and 30 and preferably between 0.5 and10.

Any fatty acids of natural or synthetic origin containing 8 to 34 carbonatoms can be converted into the desired powder-form, neutral or basicmetal soaps by the process according to the invention, saturated fattyacids preferably being used. The process according to the invention maybe used with particular advantage for reacting technical mixtures ofnatural saturated fatty acids containing 12 to 22 carbon atoms, with theproviso that the melting point of the fatty acids is below 200° C. andpreferably below 150° C. Typical examples of such fatty acids arepalmitic acid, stearic acid, behenic acid and montanic acids and alsotechnical mixtures rich in the fatty acids mentioned.

According to the invention, oxides and/or hydroxides of calcium,magnesium, cadmium, barium, zinc and/or lead known to the expert may beused as the metal oxides or metal hydroxides. According to theinvention, calcium hydroxide, magnesium oxide and/or zinc oxide is/arepreferably used. In principle, other salts of the above-mentioned metalions, such as for example the carbonates, acetates, stearates, or othermetal soaps may of course also used in the process according to theinvention.

In one preferred embodiment of the invention, diluents adapted to themetal soaps are added to regulate viscosity, particularly where fattyacids having a melting point above 100° to 150° C. are used. Suitablediluents are, for example, paraffins having a melting point of 20° to150° C. and preferably to 100° C., esters of wax acids and higheraliphatic alcohols preferably containing 12 to 22 carbon atoms,spermaceti or suitable fatty acids. The diluents according to theinvention may be mixed with the starting fatty acids in a ratio byweight of 1:10 to 10:1 and preferably 1:2 to 2:1, depending on the metalsoap, this ratio by weight being determined by the pumpability of thereactor contents.

To ensure continuous operation of the feeder, it has proved to beadvisable for the purposes of the invention to provide the screw with ananti-adhesive coating. This coating is intended to prevent adhesion orbridge formation of the metal oxide or metal hydroxide on the screwconveyor.

The process according to the invention is further optimized by the useof spray cooling in the condensation system. The superheated steam fromthe neutralization reactor is cooled in the condensation system via aninjection nozzle operated with cold process water. Under the effect ofthis spray cooling, the danger of incrustations being formed in thecondensation system is almost completely eliminated and adjustment ofthe installation pressure remains freely selectable.

The present invention relates to the use of the neutral or basic metalsoaps produced by the process according to the invention as stabilizerand/or lubricant mixtures in the processing of plastics and as a feedadditive for dairy cows.

The invention is illustrated by the following Examples.

EXAMPLES Example 1

In a 2.5 m³ reaction vessel equipped with a four-stage MIG stirrer witha base-mounted stirring element and a condensation system, 468 kgtechnical stearic acid were initially introduced with the bottom outletvalve closed and the jacket heating system was switched on. At atemperature of approximately 70° C., 411 kg glycerol distearate wereintroduced and the reaction mixture was heated with stirring to 150° C.At the same time, the installation pressure was reduced to 550 mbar.After the bottom outlet valve had been opened, the circulation pump ofthe external reaction loop and the inline mixer were switched on. Byswitching on the metering screw and opening the sealing element, 63 kgcalcium hydroxide were introduced into the premixing zone over a periodof 45 minutes. The transport capacity of the inline mixer was adjustedin such a way that, on the one hand, no excessive foaming was caused bythe return of the metal soap via the inline mixer to the reaction vesseland, on the other hand, no fatty acid flowed back into the meteringscrew. After the solid had been introduced, the installation pressurewas reduced to around 30 mbar and the water of neutralization wascontinuously removed via the condensation system. The end point of thereaction (approx. 1 hour) was determined by continuous sampling anddetermination of the acid value (required acid value: 5 to 10). Theinstallation pressure was then returned to normal pressure with nitrogenand the liquid reaction mixture was made up in the usual way, forexample by prilling. The melting point of the metal soap formed wasapproximately 95° C. for a yield of 99%.

Example 2

2800 kg technical stearic acid were introduced into and heated to around95° C. in a 10 m³ reaction vessel equipped in the same way as describedin Example 1. 2100 kg of a paraffin wax (melting point: <80° C.) werethen introduced over a period of 1 hour with the proviso that atemperature of 85° C. was not exceeded. After the reaction temperaturehad been increased to 150° C., the installation pressure was lowered to550 mbar and the external reaction loop was brought into operation viathe circulation pump and the inline mixer. 160 kg zinc oxide were thenintroduced into the inline mixer by the metering screw over a period of45 minutes. Without any interval, 213 kg calcium hydroxide wereintroduced in the same way over a period of 35 minutes without anychange in the reduced pressure of the system as a whole. After the solidhad been introduced, the installation pressure was reduced to around 30mbar and the water of neutralization was continuously removed throughthe condensation system. The end point of the reaction (approx. 1 hour)was determined by continuous sampling and determination of the acidvalue (required acid value: 5 to 10). The installation pressure was thenincreased to normal pressure with nitrogen and the liquid reactionmixture was made up in the usual way, for example by prilling. Themelting point of the metal soap formed was approximately 100° C. for ayield of 99%.

We claim:
 1. A process for the production of a solid metal soap of theformula

    M(R--COO)(R"--COO)

in which M represents at least one metal cation selected from the groupconsisting of Ca, Mg, Cd, Ba, Zn, and Pb and R and R¹ representindependently selected C₈₋₃₄ hydrocarbon radicals, by direct synthesisfrom at least one fatty acid with metal oxides and/or metal hydroxides,which comprises: maintaining a reaction zone containing a liquid phasecomprising at least one fatty acid under reduced pressure; passing aportion of the liquid phase to an external premixing zone; introducing asolid metal oxide and/or metal hydroxide into the liquid phase in thepremix zone to form a mixture; passing this mixture to the reaction zonethrough an intensive mixing zone; and continuously removing water ofneutralization formed by reaction between at least one fatty acid withmetal oxides and/or metal hydroxides from the reaction zone as a gasphase.
 2. A process of claim 1, wherein the solid/liquid reaction iscarried out under conditions wherein the premixing zone is in pressureequalization with the reduced pressure in the reaction zone wherein apaste-form mixture formed in the premixing zone serves as a sealingcompound for pressure equalization.
 3. A process of claim 1 wherein thepressure in the reaction zone is in the range from 100 to 900 mbar.
 4. Aprocess of claim 1 wherein the premixing zone is operated at a reducedinternal pressure of 400 to 900 mbar.
 5. A process of claim 1 wherein aratio by weight of the liquid phase to solid phase of 20:1 to 100:1 ismaintained in the premixing zone.
 6. A process of claim 1 wherein theintensive mixing zone comprises an inline mixer.
 7. A process of claim 1wherein the solid metal oxide and/or metal hydroxide is introduced intothe premixing zone by a screw conveyor.
 8. A process of claim 1 whereinthe at least one fatty acid comprises a mixture of natural fatty acidscontaining 8 to 34 carbon atoms with the proviso that the melting pointof the mixture of fatty acids is below 200° C.
 9. A process of claim 1wherein the metal oxide and/or hydroxide comprises at least one metaloxide or hydroxide selected from the group consisting of calciumhydroxide, magnesium oxide and zinc oxide.
 10. A process of claim 1wherein the liquid phase comprises a diluent to regulate viscosity ofthe liquid phase.
 11. A process of claim 10 wherein the diluent,comprises a paraffin having a melting point of 20° to 150° C. present inrelation to the amount of starting fatty acids in a ratio by weight of1:10 to 10:1.
 12. A process of claim 3 wherein the pressure in thereaction zone is in the range of from 200 to 800 mbar.
 13. A process ofclaim 4 wherein the premixing zone is operated at a reduced pressure offrom 750 to 850 mbar.
 14. A process of claim 8 wherein mixture of fattyacids comprises fatty acids having 12 to 22 carbon atoms.
 15. A processof claim 8 wherein the melting point of the mixture of fatty acids isbelow 150° C.
 16. A process of claim 15 wherein the mixture of fattyacids comprises fatty acids having 12 to 22 carbon atoms.
 17. A processof claim 11 wherein the diluent has a melting point in the range of 60°C. to 100° C.
 18. A process of claim 11 wherein the weight ratio of thediluent to the amount of starting fatty acid is in the range of 1:2 to2:1.
 19. A process of claim 2 wherein the pressure in the reaction zoneis in the range of 100 to 900 mbar.
 20. A process of claim 19 whereinthe pressure in the premixing zone is in the range of 400 to 900 mbar.21. A method for stabilizing a polymer composition which comprisesincorporating in the polymer composition a stability improving amount ofa product of the process of claim
 1. 22. A method for improving thenutrition of dairy cows which comprises including in feed for dairy cowsa product of the process of claim 1.